Digester and digestion process

ABSTRACT

A digestion apparatus is provided that include a vessel, a closure, and a fluid-transporting system. The vessel has a digestion chamber therein and an opening that provides access to the digestion chamber. The closure is adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber. The fluid-transporting system is adapted to direct fluid out of the digestion chamber back into the digestion chamber through an inlet port. The apparatus may include improved fluid heating, sample holding, safety and/or circulation options. Also provided are digestion methods that may use the digestion apparatus.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/533,261, filed Sep. 11, 2011, entitled “Improved Digesterand Digestion Process,” by Andrew Kallmes, the disclosure of which isincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates generally to improved digestion technology, e.g.,apparatuses and processes for digesting samples. In particular, theinvention relates to digesters that provide improved fluid heating,sample holding, safety and circulation options.

There is a substantial current need for improved apparatuses forcarrying out chemical reactions at elevated temperatures and/orpressures. Such apparatuses include, for example, digestion apparatusesthat are used to produce pulp and/or intermediate fibrous materials froma wide variety of cellulosic materials.

In general, digestion apparatuses are designed to carry out cellulosicdigestion in batch or continuous processes in a rapid manner to resultin a high yield. In a conventional batch cooking sulfite process, forexample, a digester is filled with wood chips and charged with freshcooking liquor. The digester is then sealed, and heated to cookingtemperature by direct or indirect heating. Once cooked, a substantialportion of the lignin and carbohydrates may be degraded and/or leachedfrom the pulp. Spent cooking liquor (black liquor) and the pulp areseparated after cooking.

The laboratory digester is one of the most widely used instruments inthe pulp and paper industry. The digester allows a user to experimentwith a wide range of chemical compositions to optimize the full-scalecooking process. Laboratory digesters are available in a wide range ofvolumes and may provide critical insight into the chip cooking processfor scale-up and/or optimization efforts.

A number of laboratory digesters are commercially available. Forexample, M/K Systems, Inc. (Peabody, Mass.) manufactures ahigh-pressure, vertically circulating, batch-process digester that runspulp-digesting processes on a laboratory scale in a precisely controlledmanner. Typically available in either single or dual vessel models, thedigester provides excellent control over the cooking profile,homogeneous temperature distribution due to excellent systemic flowcontrol and excellent liquor mixing. In addition, the digester issuitable for both alkaline and acid digesting process with various typesof wood chips and fiber sources. Furthermore, the digester is designedto operate at high temperatures at elevated pressures.

Certain models of digesters from M/K Systems are constructed withfeatures that improve fluid-transportation efficiency, higherpressurization, and space utilization. In addition, other features,e.g., a variety of different sample holding options, lead to improveddigestion performance. U.S. Pat. No. 7,811,416 and U.S. PatentApplication Publication No. 20100329943, both to Kallmes, describe suchfeatures and other improvements to digester technologies.

Nevertheless, there exist further opportunities to provide alternativesand improvements to sample digestion technologies. For example,improvements have been made in the areas of heating, fluid flowcharacteristics, flow path design, and sample holding options. Suchimprovements may be useful to overcome shortcomings associated withprior art cellulose digestion processes. In turn, the improvements mayaddress previously unmet and long-felt needs to improve processcapacity, precision, efficiency, and safety. In other words, theimprovements may allow materials to be digested even more precisely,with enhanced safety, at higher temperatures and/or pressures, and withgreater throughput and operator convenience.

SUMMARY OF THE INVENTION

The invention provides a digestion apparatus that include a vessel, aclosure, and a fluid-transporting system. The vessel has a digestionchamber therein and an opening that provides access to the digestionchamber. Optionally, the digestion chamber may have a lower taperedportion. The closure is adapted to interface with the vessel opening toform a fluid-tight seal against a digestion pressure and temperaturewithin the chamber. The fluid -transporting system is adapted to directfluid out of the digestion chamber back into the digestion chamberthrough an inlet port.

Some embodiments of the inventive apparatus include a fitting isprovided having at least five fitting ports in fluid communication witheach other. As least one fitting port fluid is interfaced with thevessel, closure, and/or fluid-transporting system. Typically, at leastthree fitting ports define substantially coplanar fitting passagewaysand at least two of the substantially coplanar fitting passageways arenot parallel to each other. For example, the fitting may have exteriorsurfaces that define a prism having a square or rectangular base.Optionally, a one-way valve may be interfaced with a fitting port and anadditional vessel interfaced with the one-way valve.

In addition or in the alternative, the fluid-transporting system may beadapted to direct fluid out of the digestion chamber into at least oneof first and second flow paths. The first flow path is effective toreturn fluid through an inlet port into the chamber. The second flowpath forms a bypass loop located outside the chamber that is effectiveto allow fluid to circulate therein. A valve may be provided forselectively closing one of the first and the second flow paths.

A plurality of heaters may be provided. In some instances, a firstheater in the form of a heat exchanger may be provided for heating fluidoutside the chamber for introduction into the digestion chamber, and asecond heater may be provided for heating the vessel and/or chamber.

A condenser may be interfaced with the fluid transporting system and/orchamber. In such as case, a pressure-relieving means may be providedthat allows for fluid released therefrom to drain into the condenser.The pressure-relieving means may include a rupture disk or a pressurerelief valve.

In some instances, the fluid-transporting system may be adapted todirect fluid out of the digestion chamber back into the digestionchamber through a flow path that extends, in order, through a submergedoutlet port, a filter, a pump, a conduit and an inlet port, wherein theconduit is located in the flow path immediately before the inlet port.The conduit may define a flow path that exhibits no bend having a radiusof curvature less than about 1 centimeter when the flow path has adiameter of about 1 centimeter. Similarly, the flow path from the outletport and the pump may exhibit no bend having a radius of curvature lessthan about 2 centimeters when the pump is positioned in an offset mannerbelow the outlet port and the flow path exhibits a diameter of about 1centimeter. Such systems and variations thereof may define a flow paththat ensures substantial laminar digestion fluid flow through the inletport. Optionally, the filter and the pump independently and fluidlycommunicate with a downstream drain valve that when opened allows fluidto drain simultaneously from the filter and the pump.

A rinse line may be provided in fluid communication with the inlet portvia a one-way valve (or check valve), allowing the user to connect lowpressure water to the high pressure system. The one way valve may beinstalled such that low pressure water can enter the digester, but thevalve may be closed to pressure exiting the digester. The rinse line maybe used in combination with a means for distributing fluid as a safetyand performance improvement feature.

A container may be provided within the digestion chamber. In someinstances, the container may comprise a plurality of compartments forholding a plurality of samples. For example, the container may comprisea basket and one or more dividers. In some instances, horizontaldivider(s) may define the compartments within the basket. The horizontaldivider(s) may define compartments of substantially identical shape andsize and/or may be removable from the basket. The horizontal porousdivider(s) allow the user to cook a plurality of different sampleswithin the same vessel, as liquor flows from the top section to lowersections. Additionally, one or more vertical non-porous dividers may beused to allow a plurality of samples to be cooked simultaneously withinthe same basket.

The invention also provides digestion methods. For example, a method isprovided that involves first placing a sample within a digestion chamberof a vessel. Then, a fluid may be circulated and optionally heated to adesired temperature within a bypass loop located outside the chamber.Then, the fluid may be directed out of the bypass loop through an inletport into the chamber toward the sample. The fluid downstream from thesample may then be out of the chamber and back into the chamber throughthe inlet port, optionally without returning fluid downstream fromsample to the bypass loop. Optionally, the vessel and/or chamber isheated to a desired vessel and/or chamber temperature before the fluidis introduced into the inlet port and the chamber. In any case, fluidtransported out of the chamber may be systemically re-circulated, e.g.,repeatedly heated outside the chamber, directed through an inlet portinto the chamber toward the sample, and, after contacting the sample,transported out of the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts in schematic cross-sectional view a single vesselembodiment of a digestion apparatus of the invention.

FIG. 2 depicts in schematically cross-sectional view thefluid-transporting member shown as a component of the digestionapparatus of FIG. 1 in the form of an elongate tube having perforationsalong its length.

FIG. 3 is a photograph of a container that includes a basket and aremovable dispersion weight.

FIGS. 4A and 4B, collectively referred to as FIG. 4, are photographs ofa basket container with a detachable mesh bottom. FIG. 4A shows thecontainer with the bottom attached. FIG. 4B shows the container with thebottom detached.

FIGS. 5A and 5B, collectively referred to as FIG. 5, schematicallydepict an unitary cube plumbing fitting having six ports. FIG. 5Adepicts the fitting in perspective view. FIG. 5B depicts the samefitting in cross-sectional view along the plane indicated by dotted lineA.

FIG. 6 is a photograph of a digestion apparatus of the invention similarto that depicted in FIG. 1.

FIG. 7 are photographs of an upper portion of an exemplary digestionapparatus of the invention. FIG. 7A highlights laminar fluid flowthrough an inlet port that extends through a flange. FIG. 7B highlightsthe plumbing associated with the flow path upstream from the inlet port.

FIGS. 8A and 8B, collectively referred to as FIG. 8, schematicallydepict containers having a plurality of compartments of substantiallyidentical shape and size. FIG. 8A depicts a container having across-shaped divider therein that vertically separates fourcompartments. FIG. 8B depicts a container having three horizontallyseparated compartments.

FIG. 9 is a close-up photograph that shows the location of an inlineV-filter below the vessel of an exemplary digestion apparatus similar tothat depicted in FIG. 1.

FIG. 10 is a close-up photograph that shows a conduit that forms aportion of the curved flow path between the digestion vessel and thepump of an exemplary digestion apparatus similar to that depicted inFIG. 1 except with an offset pump placement.

FIG. 11 provides a simplified depiction of digestion apparatus similarto those shown in FIGS. 1 and 6.

FIGS. 12A -12C, collectively referred to as FIG. 12, depict variousvessel designs for the inventive digestion apparatus. FIG. 12A depicts avessel design with a flat base. FIG. 12B depicts a vessel design with aconical base. FIG. 12C depicts a vessel design with a rounded base.

DETAILED DESCRIPTION OF THE INVENTION

Definitions and Overview

Before describing the present invention in detail, it is to beunderstood that the invention is not limited to specific digestionfluids or apparatus setups, as such may vary. It is also to beunderstood that the terminology used herein is for describing particularembodiments only, and is not intended to be limiting.

In addition, as used in this specification and the appended claims, thesingular article forms “a,” “an,” and “the” include both singular andplural referents unless the context clearly dictates otherwise. Thus,for example, reference to “a vessel” includes a plurality of vessels aswell as a single vessels, reference to “fluid” includes a fluid as wellas a mixture of fluids, and the like.

Furthermore, terminology indicative or suggestive of a particularspatial relationship between elements of the invention is to beconstrued in a relative sense rather an absolute sense unless thecontext of usage clearly dictates to the contrary. For example, theterms “over” and “on” as used to describe the spatial orientation of afirst item relative to a second item does not necessarily indicate thatthe first item is located necessarily above the second item. That is,the first item may be located above, at the same level as, or below thesecond item depending on the device's orientation. Similarly, an “upper”surface of an item may lie above, at the same level as, or below otherportions of the item depending on the orientation of the item.

In this specification and in the claims that follow, reference will bemade to a number of terms that shall be defined to have the followingmeanings, unless the context in which they are employed clearlyindicates otherwise:

The terms “cellulose, “cellulosic” and the like are used herein in theirordinary sense and refer to a complex carbohydrate or polysaccharidethat includes a plurality of monomeric glucose units (C₆F1 ₁₀O₅). As iswell known in the art, cellulose constitutes the chief part of the cellwalls of plants, occurs naturally in fibrous products such as cotton andlinen, and is the raw material of many manufactured goods such as paper,rayon, methanol, and cellophane.

The term “chamber” is used herein to refer to enclosable or enclosedspace. For example, a “digestion chamber” within a vessel may refer to apartially or fully enclosable or enclosed space within the vessel inwhich digestion may take place.

The term “closure” is used herein to refer to an item that closes. Forexample, a closure may take the form of a lid, plug, cap, or the like toclose an opening of a vessel.

The terms “digest,” “digestion,” and the like are used herein in theirordinary sense in the field of chemistry and refer to softening,disintegration, and/or decomposition of a material such as cellulose) bymeans of heat, chemical action, and/or the likes. Thus, the term“digestion fluid” refers to a liquid and/or gaseous substance, that iscapable of flowing, that changes its shape at a steady rate when actedupon by a force, and that aids in the softening, disintegration and/ordecomposition of a material. Similarly, the term “liquor” as used hereinrefers to a solution or other fluid used to carry out cellulosicdigestion. In any case, the terms “digester” and “digestion apparatus”are typically interchangeably used.

The term “fitting” is used herein in its ordinary plumbing sense andrefer to items having ports that may be used to connect pipe, tubing, orother conduit sections, to adapt plumbing supplies to different sizes orshapes (e.g., gender), and for other purposes, such as regulating ormeasuring fluid flow. Exemplary two-port fittings include, “elbows,”“couplings,” “unions,” “reducers,” etc. Exemplary three-port fittingsinclude “tees” and exemplary four-port fittings include “crosses.” Othercommonly available fittings include “caps,” “plugs,” “nipples,” and“barbs.”

The term “flow path” as used herein refers to the route or course alongwhich a fluid travels or moves. The term may have a synonymous meaningwith the term “line” when used in a plumbing context.

The term “fluid-tight” is used herein to describe the spatialrelationship between two solid surfaces in physical contact such thatfluid is prevented from flowing into the interface between the surfaces.

The term “in order” is generally used herein to refer to a sequence ofevents. When a fluid travels through a flow path that extends “in order”through items X and Y, he fluid travels through item X before travelingthrough item Y. “In order” does not necessarily mean consecutively. Forexample, a fluid traveling in order through items X and Y does notpreclude the fluid from traveling through item Z after traveling throughitem X before traveling through item Y.

The term “pressurized” as used herein refers to subjecting a fluid undera force per unit area greater than that which otherwise surrounds thefluid.

The term “substantially identical” as used to describe a plurality ofitems is used to indicate that the items are identical to a considerabledegree, but that absolute identicalness is not required. For example,when perforations are described herein as of a “substantially identicalsize,” the perforations' size may be identical or sufficiently nearidentical such that any differences in their size are trivial in natureand do not adversely affect the performance of the perforations'function. The terms “substantial” and “substantially” are usedanalogously in other contexts involve an analogous definition.

The term “vessel” is used herein in its ordinary sense and refers to ahollow or concave item, typically sealable, for holding fluids or othercontents.

In general, the invention relates to an apparatus for digesting acellulosic material or other sample. The apparatus includes a vesselcontaining a digestion chamber accessible through a vessel opening. Aclosure is also provided to interface with the vessel opening against apredetermined digestion pressure and temperature within the chamber. Acontainer inside the digestions chamber may be provided for holding asample. (The term “container” is generally used synonymously with“sample holder.”) A fluid-transporting system is adapted to directdigestion fluid through an inlet port and an optional fluid distributionmeans toward any sample in the container.

The inventive apparatus may include a number of novel and nonobviousfeatures that provide a number of previously unavailable digestion orother processing options. For example, a fitting may be provided havingat least five fitting ports in fluid communication with each other. Sucha fitting may be used to provide greater process flexibility, e.g., byallowing the fluid-transporting system to direct fluid out of thedigestion chamber into a main flow path and a bypass loop. In turn, thebypass loop may allow for enhanced heating process options. A smallportion of the system liquor may be directed outside of the vesselthrough the bypass loop, which could be accomplished by installing avalve to close the exit of the vessel and closing liquor which normallyis fed back into vessel. After the heater has been raised to anacceptable temperature, the liquor return line and vessel-exit valvecould be opened, allowing traditional flow, essentially starting thecook with a pre-heated heater.

Similarly, the container may be divided into a plurality ofcompartments. For example, the container may comprise a basket with aremovable porous horizontal divider that defines compartments ofsubstantially identical shape and size within the basket. Thecompartments may hold different samples so that they may undergoprocessing under same digestion conditions, one or more samples servingas a control for comparison with one or more other samples. Removablevertical dividers can also be installed, allowing the user to cookmultiple different materials within the same cooking basket.

Additional safety and/or performance enhancing features may be included.In some instances, a pressure-relieving means may be provided thatallows for fluid released therefrom to drain into a condenser interfacedwith the fluid transporting system and/or chamber. In addition or in thealternative, a rinse line may be provided in fluid communication withthe inlet port via a one-way valve. The rinse line may be used incombination with a means for distributing fluid as a safety and processcontrol feature.

As another example, the fluid-transporting system, to enhance digestionefficiency, may be constructed to direct fluid out of the digestionchamber back into the digestion chamber through, in order, a submergedoutlet port, a pump, a conduit and an inlet port. The conduit may definea flow path that exhibits no bend having a radius of curvature less thanabout 1 centimeter when the conduit has a diameter of about 1centimeter. Such systems and variations thereof may define a flow paththat ensures substantial laminar digestion fluid flow through the inletport.

The materials used to form the components of the inventive apparatus areselected with regard to physical and chemical characteristics that aredesirable for proper functioning of the apparatus. For example, allmaterials used to construct the various components of the inventiveapparatus should be chemically inert and physically stable with respectto any substance with which they come into contact when used to carryout sample digestion (e.g., with respect to pH, etc.).

Single Vessel Digestion Apparatus, Generally

An exemplary simplified single vessel apparatus of the invention isschematically depicted in FIG. 1. As with all figures referenced herein,in which like parts are referenced by like numerals, FIG. 1 is notnecessarily to scale, and certain dimensions may be exaggerated forclarity of presentation. As shown in FIG. 1, the apparatus 10 includes asingle cylindrical vessel 20 having a curved sidewall 21 bounded by agenerally planar top surface 22 and a platen base 24. Sidewall 21 isgenerally perpendicular to each of the top surface 22 and the platenbase 24. Optionally, a flange 25 extends outwardly from the top ofvessel 20 perpendicular to sidewall 21, thereby defining in part the topsurface 22 of the vessel 20. An opening 26 at the top surface 22provides access to digestion chamber 30 within vessel 20. Typically, theopening 26 is sized and shaped allow facile transport of a container 60containing materials into and out of the chamber. Optionally, the sizeof the opening has a cross sectional area equal to or greater to thecross-sectional area of any other portion of the chamber 30 along anaxis perpendicular to the opening. Also optionally, markings (not shown)may be present on an interior surface of the sidewall 21 to as toprovide a visual fill-marking that indicates the level to whichdigestion fluid may be filled for optimal performance.

As shown in FIG. 1, a groove 27 is located on the top surface 22 of thevessel 20. While the groove 27 is shown as generally circular in shape,alternative embodiments of the invention may include grooves of any of anumber of cross-sectional shapes. Seated within groove 27 is elasticring 28 having a shape that generally conforms to the groove 27.Optionally, one or more additional concentric grooves and rings (notshown) may be provided on surface 22 as well. Further optionally,sealing gasket materials may be used in the place of elastic ringsand/or grooves (also not shown).

Also provided is a closure 40 in the form of a lid having substantiallyparallel upper and lower planar surfaces indicated at 42 and 44,respectively. Lid 40 may be placed over opening 26 such that lowersurface 44 faces top vessel surface 22 and that elastic ring 28 isinterposed between surface 44 and 22. When the lid 40 is urged togetherwith flange 25 applied using clamps (not shown), the ring 28 may becompressed between surface 22 and 44. As a result, a fluid-tight sealmay be formed between the lid 40 and the vessel 20. As lid 40 may weighon the order of 10 kg, operators of the digestion apparatus mayappreciate a handle or other means (not shown) for facile manipulation,reorientation, and/or movement the lid. Optionally, such a handle may bethermally isolated such that the operator may not need to use heavygloves when using the handle to manipulate, reorientation or moving thelid.

A container 60 may be placed within the digestion chamber 30 throughopening 26 located in top planar surface 22 of the vessel 20. Whensealed within the digestion chamber 30, the container 60 may serve tohold a cellulosic material therein for digestion by digestions fluidswithin the chamber. As shown, the container 60 formed from a cylindricalbasket having an opening 62 at its top through which cellulosicmaterials may be loaded into the container 60. The container 60 has ashape and size generally similar to that of the chamber 30 to reducedead space within the chamber 30 in which no cellulosic digestion may bedigested. Optionally, a handle 64 may be attached to the opposing pointson the sidewalls near the top of the container 60 to allow a user aconvenient means for maneuvering the container 60 in and out of vessel20.

The container 60 typically also has a bottom 66 containing one or moreholes 68 through which digestion fluid may flow. As shown, the bottommay be formed from a wire mesh, but any perforated bottom may generallybe used with the invention as long as the holes 68 are appropriatelysized and located. For example, the one or more holes 68 are typicallysized to ensure that cellulosic material within the container 60 remainswithin the container before, during, and after exposure to digestionfluid within the chamber 30. Often, the holes are arranged in an array.Optionally, the sidewalls of the container 60 may also contain holes ofappropriate size and arrangement.

Further optionally, as shown in FIG. 4, the bottom 66 of the containermay be detachable from the sidewalls. In some instances, a plurality ofmodularly interchangeable bottoms with different mesh sizes and/or holearrangements may be provided so that they can be used with the samecontainer. That way, the container may better retain samples therein atall stages of digestive state while allowing for appropriate or optimaldigestion fluid flow therethrough, as discussed below.

In some instances, the container may vary in volume according to achange in digestive state of any cellulosic material contained therein.For example, a perforated fluid-dispersion weight 70 in the form of adisk having generally opposing parallel upper and lower surfacesindicated at 72 and 74, respectively. The weight also contains an arrayof holes 76 extending through surfaces 72 and 74 that provides aplurality of flow paths through which fluids may travel. In other words,the weight 70 is effectively rendered porous for digestion fluidflow-through. The disk 70 is shaped and sized to allow it to be placedin movable relationship with container 60. Optionally, a handle 78attached to upper surface 72 may be provided to allow for facilehandling of the weight 70. An exemplary basket and dispersion weightsuitable for use with the invention is shown in FIG. 3. Optionally, thecontainer may allow for an extension component to increase thecontainer's capacity.

In operation, cellulosic material may be placed within the container 60,and the porous weight 70 may be placed over the cellulosic material withlower surface 74 facing the cellulosic material and the bottom 66 ofbasket 60. As a result, the effective volume of the basket 60 forcontaining cellulosic material is bounded by the basket 60 and theweight 70. As the digestive state of the cellulosic material in thebasket changes, the spatial relationship between the basket and theweight may change as well. As a result, the container 60 may effectivelyvary in volume according to the cellulosic material in the basket.Typically, as cellulosic material is digested, the mechanical strengthof the material is decreased. The weight 70 will tend to compress orcompact the cellulosic material as its physical integrity degrades,thereby reducing the effective volume of the basket.

The apparatus also includes a fluid-transporting system for transportingdigestion fluid within the digestion chamber. The fluid-transportingsystem serves to direct digestion fluid through a port and the containertoward any cellulosic material in the container. In some instances, thefluid-transporting system may be adapted to direct digestion fluid froma supply exterior to the digestion chamber toward the cellulosicmaterial therein in the container. In addition or in the alternative,the fluid-transporting system may be adapted to direct digestion fluidfrom a supply within the chamber toward the cellulosic material.

As shown in FIG. 1, the fluid-transporting system may include aplurality of components that are interfaced with the digestion vessel 20and/or chamber 30 via a plurality of ports (inlet port, outlet or othertypes of ports) through the vessel 20 and the lid 40. For example, aliquor inlet port 102 traverses through the vessel flange 27. A liquoroutlet port 108 is located in the base 24 of the vessel 20. Additionalcomponents of the apparatus shown in FIG. 1 external to the vessel 20that may be considered components of the fluid-transporting systeminclude, for example, fitting 300, pump 110, flow meter 310, conduits320, 322, 324, 326, 328, and valves 109, 112. Fitting 300 provides fluidcommunication between port 108 and conduit 320. Pump 110 provides adriving force to provide fluid flow, and flow meter measures fluid flowin the fluid-transporting system. Drain 200 fluidly communicates withthe branching conduit 322 via drain valve 118.

Filter 121 may be used to ensure that the fluid-transporting system doesnot become clogged from digested material that may escape from thesample holder. As shown in FIGS. 1 and 9, a filtering means is providedin the form of a commercially available inline V-filter 121 with a coilhollow filtration (indicated by dotted lines in FIG. 1), with filtermounted inline with the liquor flow such that liquor flows from thevessel, over the hollow wire mesh and into the pump. Another line of theV-filter may be used to drain off fine particular matter, e.g., strayfibers, after a digestion process is completed, thereby avoiding theneed to clean out the pump of contaminants which could interfere withpump's proper functioning. The filter 121 is downstream from outlet port108 and upstream from pump 110. The filter may serve to capture strayfibers and the like, thereby preventing them from reaching the pump.

Furthermore, additional components within the chamber 30 may also beinterfaced to the fluid-transporting system as well. For example, ameans for distributing fluid may be located downstream from the inletport. As shown in FIG. 1, a digestion fluid distributing means 130 inthe form of fluid-conveying member or dispersion nozzle may be connectedto liquor inlet port 102 via conduit 124. As shown, the nozzle 130 maybe mounted to lid 40, but such mounting is not required. The nozzle 130is oriented such that emerging fluid is directed toward the basket 20and the weighted disk 70 located therein. As shown in FIG. 2, thedispersion nozzle 130 formed from a straight elongate tube 131 having alumen 132 extending from an open proximal inlet port terminus 133 to aclosed distal terminus 134. A plurality of circular perforations 135 ofsubstantially identical shape and size may be arranged in a singleequidistant linear array along the length of the tube. The perforations135 extend through the wall of the tube 131. The proximal terminus 133constructed to be attachable directly to a port or indirectly via aconduit to the port. U.S. Pat. No. 7,811,416 and U.S. Patent ApplicationPublication No. 20100329943 describes other possible nozzle designs.

A plurality of flow paths is shown. A drain flow path allows fluid drainfrom the lower portion of the chamber 30, in order, through outlet port108, valve 109, fitting 300, conduit 320, filter 121, pump 10, conduit322, valve 118, drain 200, and out of apparatus 10. Circulatory flowpath allows fluid from the chamber 30, in order, through outlet port108, valve 109, fitting 300, conduit 320, filter 121, pump 10, conduits322, conduit 324, flow meter 310, conduit 326, control valve 112,conduit 328, inlet port 102, conduit 124, nozzle 130, opening 62 orbasket 60, holes 76 of weight 70, and holes 68 in the bottom 66 of thebasket 60, and back into the bottom of the chamber 30.

The apparatus 10 typically also includes a heat exchanger 140 and atemperature detector 150 for measuring fluid, e.g., liquid, temperaturesin the fluid-transporting system as well. The heat exchanger may be usedto heat and/or cool fluid in the fluid-transporting system. For example,a cooling jacket may be placed around a heater to form the heatexchanger. When water is fed through inputs of the cooling jacket andthe heater is turned off, the jacket effectively converts heater into acomponent of a cooler. The placement of the heat exchanger 140 and thedetector 150 may be selected to ensure their optimal performance, e.g.,to provide uniform heating and rapid detection response. For example,the heat exchanger and temperature detector may generally be placedanywhere along the circulatory flow path, as long as the heat exchangerand temperature detector do not interfere with each other's performance.As shown, the temperature detector 150 is interfaced with fitting 300and the heat exchanger 140 is located between conduits 322 and 324,i.e., downstream from the pump 110 and upstream from the flow meter 310.As discussed below, band heaters wrapped around the vessels may be usedas a secondary or primary source of heating for the digestion apparatus.

Additional vessel ports or “nipples may be present. Typically, a vesselmay have three or four ports to facilitate access by interrogativeinstrumentation and other accessories. For example, a first pressureinterface port 104 is shown disposed near the top of sidewall 21. Asecond pressure interface port 106 is disposed through lid 40. Pressureinterface ports may be used to provide an interface with components thatact in response to pressures present in the chamber 30. For example, thepressure release valve 116 is connected with the second pressureinterface port 106, which allows vapor communication between thepressure release valve 116 and the chamber 30. The pressure releasevalve allows for controlled venting of the chamber 30 to ensure controlover pressure therein.

Similarly, port 94 is also shown disposed through lid 40. Sensor 92within port 94 provides a means for measuring vapor temperatureand/pressure within the chamber 30. Optionally, as shown in FIG. 7B,sensor 92 may disposed through other parts of the digestion apparatus,e.g., the flange 25.

The rupture disk 114 is shown connected with the first pressureinterface port 104, which allows vapor communication between the rupturedisk 114 and the chamber 30. The rupture disk 114 has a first surface115 in vapor communication with chamber 30 via interface port 104 and anopposing second surface 117 that faces a conduit 202 that fluidlycommunicates with a condenser 400. The disk 114 serves as a safetymechanism to ensure that any excessive pressure buildup in the chamber30 does not lead to explosive or catastrophic failure of the apparatus10. For example, a rupture disk may be provided that ruptures at apredetermined pressure limit that is slightly higher than a peak desiredprocessing pressure. Thus, when the peak desired processing pressure is300 pounds per square inch (PSI), rupture disks that vent at 310 PSI maybe used.

The digestion apparatus may vary in construction. For example, FIG. 6 isa photograph of an exemplary digestion apparatus. From casualinspection, it should apparent that the digestion apparatus of FIG. 6 issimilar to but not identical to that depicted in FIG. 1.

FIG. 11 shows that the inventive apparatus may include other componentsas well. For example, a liquor insertion tank 700 may be provided. Asshown, a flow path may be created from the liquor insertion tank 700 tothe pump 110, via, in order, line 702, valve 404, and conduit 320. Sucha flow path allows the pump draws in liquor rather than wait for liquorto creep in via head pressure alone.

FIG. 11 also show how two different flow paths are created at V-filter121. A first flow path begins at conduit 320, and a second flow pathbegins at conduit 321. It has been observed that, when the flow pathsterminate at different drain valves, operators often forget to open bothvalves for proper cleaning and maintenance. Thus, a combined drain linerepresents another novel and nonobvious aspect of the invention. Asshown in FIG. 11, the first flow path extends through conduit 320 andpump 110 before reaching conduit 322 and drain valve 118, whereas thesecond flow path extends through conduit 321 to reach conduit 322 anddrain valve 118 in a manner that bypasses pump 110. In other words, bothconduits 320 and 321 fluidly communicate with drain valve 118. Thecombined drain line ensures that whenever the pump is cleaned anddrained via drain valve 118, the filter 121 is drained via drain valve118 as well.

Exemplary Digestion Process And Parameters, Generally

In operation, the digester 10 shown in FIG. 1 may be used to effectdigestion of cellulosic and other samples in the manner described below.While the inventive digestion process is generally described below ascomprising a plurality of steps to be carried out in succession, one ofordinary skill in the art will recognize that at least some of thesesteps may be carried out in an overlapping or simultaneous manner. Theorder in which the steps are carried out may vary as well.

As an initial matter, the digester may be used to digest any material.However, materials that are of substantial or high cellulosic contentare generally preferred. Exemplary cellulosic materials include, woodchips, raw cotton, hemp, flax, bamboo, methanol preparation, numerousbiomaterial preparations, etc. However, the digester may be optimizedfor use with a particular material. For example, the holes 68 in thebottom 66 of basket 60 may be of a sufficiently large size to as toallow for uninhibited fluid through flow but of a sufficiently smallsize to ensure containment of material loaded therein. A sample may beplaced through opening 62 into basket 60, followed by porous weight 70.Care should be taken to ensure that the weight 70 is positioned in amanner that that allows for it to move and compress or compact thesample as the bulk volume and mechanical strength of the materialdecreases through digestion. This may involve placing the weight 70 suchthat its lower surface 74 faces and is substantially parallel to thebottom 66 of basket 60. A user may then use the handle 64 to maneuverthe basket 60, bottom 66 first, into the chamber 30 through chamberopening 26.

Digestion fluid may then be introduced into the chamber 30. Depending onthe digestion chemistry desired by the user, any of a number ofdigestion fluids may be used. For example, the digestion fluid may bebasic or acidic in nature and have a pH ranging from zero to 14. Theacidity/alkalinity may be measured and/or recorded by using a pH meter.Similarly, the fluid may include oxidizing and/or reducing agentsselected according to the sample in the basket 60. In any case, it istypically desirable to ensure that the drain valve 118 is closed beforethe digestion fluid is introduced into the chamber 30. Additionally,strong oxidizing agents such as ozone can also introduced through aone-way check valve into the vessel and/or fluid transporting system.The one-way check valve ensures fluid flow in one direction: the vesselpressure cannot exit out, while fluids can be introduced into thesystem. As discussed elsewhere herein, one-way check valves may beinstalled into the vessel closure or into the multi-connector below thevessel.

In some instances, the digestion fluid may be introduced into thechamber via opening 26. In such a case, the system power may be off.However, digestion fluid in some embodiments may be introduced into thechamber through the liquor inlet port 102 from a source (not shown)through pumping action effected optionally by pump 110.

The volume of digestion fluid added may vary according to the design ofthe inventive apparatus and other factors such as the volume andchemistry of the sample to be digested. Exemplary volumetric ratios ofdigestion fluid to sample may range anywhere from 1:2 to 2:1 to 5:1 to10:1. In addition, a sufficient amount of digestion fluid may beintroduced into the chamber 30 so that at least a portion of the sampleand the outlet port 108 are submerged. Optionally, the weight 70 may besubmerged as well. However, it is generally desirable to avoidintroducing an excessive volume of digestion fluid into the chamber 60so as to interfere with the workings of rupture disk 114 and thepressure control valve 112. These components typically require space tobe allocated for vapor compression. Accordingly, it may be undesirableto submerge the first and second interface ports, 104, 106,respectively.

Before the chamber 30 is sealed, it may be desirable to operate the pump110 in a purely circulatory manner without either the nozzle 130 or theconduit 124 connected to liquor inlet port. Typically, fluid from thechamber 30 may be directed to displace any gas within conduits in thesecond fluid flow path using the pump 110 at a low speed to distributedigestion fluid systemically throughout the apparatus. As a result,overall fluid level in the chamber 30 may be lowered and trapped gasbubbles within the flow path, e.g., in the outlet port 108, thecirculation pump 110, conduit 120, control valve 112, or inlet port 102that contribute to irregular fluid flow may be displaced. In short, suchpumping action effectively primes and/or warms up the apparatus forsmooth sample digestion in a controlled operation.

Once the apparatus has been primed and/or warmed up, conduit 124 may beattached to nozzle 130 and the inlet port 102, and the chamber 30 may besealed in a fluid-tight manner against a predetermined digestionpressure and temperature within the chamber. Depending on the conditionsrequired to carry out a desired sample digestion operation, thepredetermined pressure and temperature may vary. Typically, sampledigestion requires both heat and elevated pressure. Exemplary pressuressuitable for effecting industrial cellulosic digestion are typically onthe order of 50 to about 500 PSI, though higher pressures are oftenpreferred over lower pressures. Thus, the predetermined pressure may beno less than about 100 to about 180 to about 200 to about 300 PSI.Exemplary temperatures suitable for digest cellulosic materials inpractice are typically about 50 to about 300° C. Thus, the predeterminedtemperature may be no less than about 100 to about 200° C.

For the apparatus 10 shown in FIG. 1, lid 40 may then be placed over thevessel opening 26 so as to form the fluid-tight seal against thepredetermined digestion pressure and temperature within the chamber. Lid40 may be placed over opening 26 such that lower surface 44 faces topvessel surface 22 and that elastic ring 28 is interposed between surface44 and 22. Optionally, vacuum grease or some other sealing compound maybe applied to the elastic ring 28 and/or portions of surfaces 44 and 22,which may come into contact with the elastic ring. Clamps 50 are thensecured to the lid 40 and flange 25 to compress ring 28 so as to form afluid-tight seal.

Other means may be used to provide a fluid-tight seal as well.Typically, a fluid-tight seal involves the immobilization of the lid 40to the vessel flange 25. When corresponding holes are present in the lidand vessel flange (not shown), bolts may be extended through thecorresponding holes to urge the lid and flange together. In someinstances, alternative or additional external means may be used to urgethe pieces together (such as clips, tension springs or associatedfastening apparatus). Other means such as male and female couplings orfriction fittings may be advantageously used as well. Releasableadhesives such as those in the form of a curable mass, e.g., as a liquidor a gel, may be placed between the substrates and subjected to curingconditions to form an adhesive polymer layer therebetween. Additionalreleasable adhesives, e.g., pressure-sensitive adhesives orsolvent-containing adhesive solutions may be used as well.

Once the chamber 30 is sealed, the heat exchanger 140, in heating mode,and the pump 110 may be used to cook the sample in the basket 60 in acontrolled pressurized environment. Optionally, steam may be introducedinto the digester before cooking. The heat exchanger 140 may be used toheat any digestion fluid in contact therewith and may be controlledusing feedback from the temperature detector 150 and/or sensor 92.Depending on the desires of the user, the heat exchanger 140 may becontrolled on the fly or follow a preprogrammed cooking profile. Sincethe volume in the chamber 30 remains constant while the temperaturetherein increases, pressure in the chamber 30 increases as well.Optionally, steam or another gas may be introduced into or extractedfrom the chamber 30, e.g., via control valve 112, while the chamber 30is sealed so as to ensure that the pressure in the chamber 30 ismaintained within in an optimal range for sample digestion withoutcompromising safety.

Simultaneously, the pump may direct digestion fluid to baste the samplein the basket while the material is cooked. Because the bottom of thechamber is filled digestion fluid, that fluid represents a supply, whichmay be used to baste the sample in the basket. In operation, the pump110 draws fluid from the supply at the bottom of the chamber throughoutlet port 108 via valve 109 into the pump 110. Then, fluid is forcedthrough the conduit 120, control valve 112, inlet port 102, conduit 124,toward the nozzle 130.

Notably, the position of pump 110 may affect the operation of thefluid-transporting system. As shown in FIGS. 1 and 6, pump 110 may beplaced directly below outlet port 108. It has been experimentallydemonstrated that a digestion apparatus having a pump located directlybelow the apparatus' outlet port tends to perform better than a similardigestion apparatus having a similar fluid-transporting system designthat uses an offset pump location. An offset pump placement tends tolead to cavitation and other problems absent in fluid transportingsystems with a pump placement shown in FIGS. 1 and 6.

However, it is possible to avoid cavitation and other problemsassociated with an offset pump placement. For example, it has beenobserved cavitation and similar pump problem occur when fluid is fed tothe pump in an inadequate manner, e.g., with an unsteady, irregularand/or nonlaminar flow. To reduce such flow for an offset pumpplacement, sharp turns, e.g., those associated with 90° elbow and teeshaped fittings should generally be avoided in the flow path from theoutlet port 108 and the pump 110. Instead, as shown in FIG. 10, aconduit 320 forming gently curving flow path of appropriatecross-sectional area may be employed to deliver substantially gas freeliquid to a pump 110 located with an offset placement relative to theoutlet port of the digestion vessel. Additional digestion fluidtransportation issues as they relate to apparatus performance arediscussed below.

Digestion fluid is directed through the open proximal inlet portterminus 133 at a flow rate and pressure effective to allow thedigestion fluid to occupy the entire lumen 132 or substantially theentire lumen 132. Consequently, pressurized digestion fluid is sprayedout of the perforations 135 at a velocity higher than that would beachieved from gravitation forces alone. Fluid emerging from the nozzle130 is distributed toward the sample through the holes 76 of weight 70.Instead of merely flowing toward the sample under gravitational andsurface forces, the nozzle 130 effectively concentrates fluid flowingtherefrom into focused streams that increases the rate at whichdigestion fluid penetrates the sample. As a result, use of the nozzle130 effectively increases sample digestion efficiency over the digestionefficiency that would be achieved without the nozzle.

Sample so sprayed in a digestion chamber typically exhibits a higherdegree of digestion than sample exposed to digestion fluid under thesame conditions but under gravitational forces alone.

As a result of exposure to elevated temperature, elevated pressure, andcontinuous exposure to circulated (refreshed) digestion fluid, thesample in the basket 60 may be digested to a desired degree. As thesample is digested, its physical integrity will become increasinglycompromised. As a result, the weight 70 will typically move toward thebottom 66 of the basket 60 and compress or compact the sampletherebetween. Once the desired degree of digestion is achieved, the heatexchanger run in cooling mode to cool off the apparatus. Alternatively,the heat exchanger and/or pump may be turned off to allow the apparatusto cool. Once cooling has taken place, the apparatus may be drained andcleaned.

It should be noted that a number of process digestion processes may bemonitored while they are taking place. For example, it is generallydesirable to ensure that the fluid flows within the fluid-transportationsystem at a substantially constant pressure and/or flow rate. Spikes inpressure and/or flow rate may indicate a less than optimal digestionperformance.

In addition, vapor and liquid temperatures may be independent monitored.Such independent temperature monitoring involves employing differenttemperature monitoring/detection means at different locations of thedigestion apparatus. Generally, the vapor temperature may be measuredusing a sensor that does not come into directed contact with the liquor,e.g., in a location above the liquor circulation path. Such a sensormay, for example, be placed in the closure, flange, or upper sidewall ofthe chamber. In contrast, the liquid temperature is typically measuredusing a sensor that does come into direct contact with the liquor. Sucha sensor, for example, may be placed at the lower portion of the chamberor in the fluid-transporting system.

In any case, as shown in FIG. 1, the circulating liquor temperature maybe monitor using detector 150 while the vapor temperature may bemeasured using temperature sensor 92. It should be noted that it may bedesirable to carry out a digestion process in a manner that ensures thatthe measured vapor temperature does not exceed the measure temperatureof the circulating liquor. When the measured vapor temperature spikesabove the measured liquor temperature, such spiking may be attributableto localized generation of superheated vapor, an artifact of unevenheating and inhomogeneous digestion reactions. Accordingly, a signalgenerator be employed to generate a signal when the measured vaportemperature exceed the measure digestion fluid temperature. Such asignal may be used to alert a digester operator to suboptimal digestionprocess conditions or to control various components of the digestionapparatus, e.g., open or close valves, increase or decrease power toheaters, etc.

Unitary Fitting with a Plurality of Fitting Ports

Space utilization of digestion apparatuses is an important issue becausemany digestion processes may take hours or days. Because laboratoryspaces are often limited, there may be only enough space for onedigester for a particular laboratory. In such instances, a digester of aparticular size having the capacity to process a larger sample volumeper run may be preferred to a digester of the same size but having thecapacity to process a smaller sample volume per run. For example, it isgenerally desirable to use a sample container having a larger volumetriccapacity within the digestion chamber than a smaller sample container.In addition, it is generally desirable to provide minimize the volumeoccupied by fluid and/or plumbing outside the vessel chamber of thedigestion apparatus.

Nevertheless, there is an increasing need to interface more accessoriesand fixtures with digestion apparatuses to improve performance andenhance safety. As shown in FIG. 1, such accessories and fixtures mayinclude, for example, sensors 92 such as pH meters, detectors 150,valves 116, and pressure relieving means such as rupture disks 114.Often, it is impracticable to drill additional ports in the vesseland/or closure after the vessel and/or closure has been manufactured.

Persons of ordinary skill in the art would recognize that a unitaryfitting having numerous ports may be used to replace an assembly offittings each having fewer ports than the unitary fitting. For example,a cross may be replaced with an assembly of two tees. Similarly, thesix-port cube-shaped fitting 300 shown in FIG. 5 may sometime befunctionally duplicated by assembling four tees, each having threeports. However, the fitting in FIG. 5, as is the case with other unitaryfittings in general, will typically occupy less volume than an assemblyof fittings each having fewer ports. In turn, the number of connectionsand tubing may be reduced, thereby resulting in significantly lessliquor outside of the cooking vessel itself

Accordingly, a unitary fitting having a large number of fitting ports influid communication with each other in combination with digestionsapparatuses represents a novel and non-obvious improvement relative tothe prior art. Such a fitting generally allows for the digestionapparatus to retain a higher proportion of fluid within the vessel,e.g., in contact with the sample or container (sometimes referred to asthe cooking substrate). The fitting may also minimize the out-of-vesselcooking liquor by reducing the number of connectors and excess tubing.

FIG. 5 depicts a unitary cube-shaped fitting 300 have six ports 302 thattraverse each substantially planar exterior surface of the fitting. Sucha fitting may be used with the fluid-transporting system associated withdigestion apparatuses. As shown in FIGS. 1 and 6, the fitting 300 mayhave ports interfaced with one or more of the following—outlet port 108,detector 108, conduit 402, conduit 320, and valve 500.

Optionally, the fitting may have another port (not shown) interfacedwith a one-way valve to allow for fluid transfer between chamber 30 ofvessel 20 and an additional vessel (not shown), e.g., via a pressuredifference between the vessels, to form a dual vessel apparatus. Forexample, certain embodiments of the invention may include two or morevessels. For such and other embodiments with two more chambers, a liquortransfer option may be provided to allow a user a convenient means totransfer liquids and vapor from a higher-pressure vessel to a lowerpressure vessel. Typically, such transfer takes place when system and/orpump power are off Valves between flow paths connecting the vessels areopened, and fluid transfer may continue until pressure is equalizedbetween the vessels or until a valve is closed in the flow path.

In addition, the locations of the ports through which inter-vessel fluidtransfer can vary. For example, fluid may exit a fitting port locatedbelow and in fluid communication with a first vessel at a high pressure,travel through a connector hose, and enter a second vessel at a lowpressure via a port that traverse through a closure atop the secondvessel or a flange of the second vessel. Similarly, fluid may exit afirst vessel at a high pressure via a port that traverses through aclosure atop the vessel or a flange of the second vessel, travel througha connector hose, and enter a second vessel at a lower pressure via afitting port located below and in fluid communication with a secondvessel. To facilitate ease of use, the connector hose may be flexible.

In any case, a fitting having numerous fitting ports may be interfacedvia at least one of the port to the vessel, closure, and/orfluid-transporting system. More generally, the fitting may have at leastthree fitting ports define substantially coplanar fitting passageways.Sometimes, at least two of the substantially coplanar fittingpassageways may not be parallel to each other. In some instances nosubstantially coplanar fitting passageways is a parallel to another.

The exterior surfaces of such a fitting may vary. For example, thefitting may have exterior surfaces that define a prism. As depicted inFIG. 5, the fitting may have a square base. However, bases of othershapes, e.g., rectangles, pentagons, hexagons, octagons, etc. may beused as well.

Heating Options

The invention also includes a number of heating options that representan improvement over previously known vertically circulating digesters.One area involves preheating. In general, previously known digesters donot allow for a preheating option. As discussed above, the digestionprocess typically begins when the sample and digestion fluid are loadedat room temperature into the digestion chamber of the vessel. Once theclosure is interfaced with the vessel opening to form a fluid-tight sealagainst the chamber, the fluid transporting system and the heatexchanger is activated so that digestion fluid is directed fluid out ofthe digestion chamber into a flow path where the fluid may be heated bya heat exchanger before reintroduction into the chamber. Accordingly,the sample must initially soak in the digestion fluid at roomtemperature before the fluid heated to a desired cook temperature. Thatis, sample soaking and heating steps of a digestion process areeffectively coupled to each other and may not be carried outindependently from each other.

In contrast, the invention provides a number of options that a digestionprocess to with decoupled sample heating and sample soaking steps. As afirst heat-soak decoupled option, the digestion apparatus may have afluid-transporting system that may direct fluid out of the digestionchamber one or more different flow paths. For example, thefluid-transporting system may direct fluid into at least one of firstand second flow paths. The first flow path may be a main circulatoryflow path that is effective to return fluid through an inlet port intothe chamber. The second flow path may form a bypass loop located outsidethe chamber that is effective to allow fluid to circulate and be heatedtherein. Typically, a valve is included for selectively closing one ofthe first and the second flow paths. Similarly, a heater may be providedfor heating fluid in a section shared by the first and second flowpaths.

In operation, a sample is placed within the digestion chamber. The fluidmay be first circulated within the bypass loop and then directed out ofthe bypass loop through an inlet port into the chamber toward thesample. Finally, the fluid downstream from the sample may be directedout of the chamber and back into the chamber through the inlet port,typically without returning fluid downstream from sample to the bypassloop. Optionally, fluid may be heated within the bypass loop to apredetermined and/or desired temperature effective to allow the fluid todigest the sample before being directed back into the chamber. Closingvalves to stop fluid from exiting the chamber and closing the re-entryvalve maintains flow inside the bypass loop. This heats the systemfaster.

Turning to FIG. 1 for example, fitting 300 provides a means for formingthe first and second flow paths as described above. The first flow pathmay serve as a main circulatory flow path that extends in order throughchamber 30, outlet port 108, valve 109, fitting 300, conduit 320, filter121, pump 110, branching conduit 322, heat exchanger 140, conduit 324,flow meter 310, branching conduit 326, valve 112, branching conduit 328,inlet port 102, conduit 124, and nozzle. Valves 404, 118, 500, and 602are closed to ensure that fluid traveling through the first flow path isnot diverted. In contrast, the second flow path may form a bypass loopthat extends through fitting 300, conduit 320, filter 121, pump 110,branching conduit 322, heat exchanger 140, conduit 324, flow meter 310,branching conduit 326, and valve 500. Valves 109, 404, 118, and 112 maybe closed to ensure that fluid remains in the bypass loop. Preferably,drain valve 118 may be located downstream from pump 110.

In addition or in the alternative, the digestion apparatus may beconstructed to comport to a second heat-soak decoupled option in which aplurality of heaters and/or heat exchangers are included. For example, afirst heater may heat fluid outside the chamber for introduction intothe digestion chamber, and a second heater may directly heat the vesseland/or chamber. When, as shown in FIG. 1, the second heater 90 is a bandheater wrapped around the vessel, the second heater may indirectly heatfluid inside the chamber. In contrast, when the second heater is locatedwith the chamber, the heater may directly contact fluid within thechamber to effect heating.

In any case, it should be noted that a band heater that is wrappedaround the vessel may serve as a secondary heater. Such a band heatermay also replace an inline heater exchanger. The band heater may heatthe vessel directly, the vessel representing the largest source of metalin the system, which in turn heats the liquor in the vessel.

In operation, a sample is placed within a digestion chamber of a vessel,and the chamber and/or vessel is heated with substantially no fluidtherein. That is, the sample may not be initially submerged within fluidin the chamber as the chamber and/or vessel is heated. Once the chamberand/or vessel is heated, e.g., to a predetermined or desiredtemperature, fluid may be directed through an inlet port into thechamber toward the sample. Then, fluid downstream from the sample may bedirected out of the chamber, optionally for reintroduction into thechamber toward the sample.

The above-described heat-soak decoupled options may be employedindependently from or in conjunction with each other. For example, fluidmay or may not be introduced through the inlet port until the vessel,chamber and/or fluid is heated to a desired temperature.

In any case, any of a number of heaters and detectors may be used withthe invention. For example, the heater include an electrically poweredresistive heating element and/or use gaseous, liquid, or solidcombustion technologies known in the art that carries out heat transferthrough conduction, convection and/or radiation. Exemplary temperaturedetectors suitable for use with the invention include thermocouple,photodiode, and other technologies known in the art. An optionalprogrammable controller (not shown) may be provided that uses signalfrom the detector to control output from the heater so as to ensure thatthe chamber's temperature and pressure conforms to a desired profile.Such controllers are widely available and may be obtained from numerouscommercial vendors, e.g., Omega (Stamford, Conn.).

Rinse Line

As alluded to above, laboratory digestion apparatuses are often used toprepare samples for experiments involving cellulosic materialsassociated with the pulp paper industry. Sample preparation wouldtypically involve first carrying out a digestion cooking process. Such aprocess may begin by placing a sample at room temperature in acontainer. Then the container may be placed in the digestion chamber ofa vessel, and the digestion chamber may be filled with digestion fluid.Once the chamber is sealed with a closure, the digestion fluid may beheated and circulated in a matter such that a steady stream is directedthrough an inlet port into the chamber toward the sample. As a result,the chamber itself will become hot and pressurized during the cookingprocess.

Eventually, heat will cease to be applied. However, components of thedigestion apparatus typically remain hot, e.g., at a temperature thatexceeds about 100° C., for an extended period. In addition, the vesseltypically remains pressurized until the vessel has cooled. As a result,only after the digestion apparatus has cooled to a manageabletemperature, e.g., less than about 100° C., would an operator attempt toremove the sample container from the digestion chamber. In someinstances, the apparatus may take hours to cool, though a heat exchangermay be used to cool the digestion fluid as it continues to circulate inthe digestion apparatus.

Typically, the cooking process does not represent the final step insample preparation. Instead, after the sample container is removed fromthe digestion chamber, the container is typically placed in a sink andrinsed with cold water. The rinsing step is typically carried out tofurther cool the sample and to remove any unwanted residue, e.g.,digestion fluid or unwanted reaction product such as lignin andcarbohydrates.

Thus, in another embodiment, the inventive digestion apparatus mayinclude a rinse line. As shown in FIG. 1, the rinse line 600 may beprovided fluid communication with the inlet port 102 via a one-way checkvalve 602 and branching conduit 328. The check valve 602 allows a rinsefluid such as low pressure water to be introduced into the digestionchamber 30 while preventing digestion fluid such as liquor or vaporunder high pressure from leaving the digestion apparatus via the rinseline.

In operation, the rinse line may be used after a desired digestioncooking process has taken place. Instead of waiting for the digestionapparatus to cool, an operator may drain the digestion apparatus ofdigestion fluid while the apparatus remains hot. Then, the rinse line600 may be used to introduce cold water or some other fluid through theinlet 102, conduit 124 and nozzle 130 to rinse the sample in thedigestion chamber 30.

The rinse line 600 provides a number of processing advantageous overpreviously known digestions apparatuses without a rinse line. As aninitial matter, sample cooking and rinsing steps had to be carried outseparately, i.e., in the digestion apparatus, and in a sink,respectively. In contrast, the addition of a rinse line allows theoperator to carry out the sample cooking and rinsing steps in the samedigestion vessel chamber without the need to relocate the sample. Thisis advantageous because hot digestion fluid residue may be present onthe cooked sample and the container, thereby representing a safetyhazard. Additionally, the rinse line can also clean off portions of thedigester system such as rupture disks, increasing their longevity. Whenleft un-cleaned, residual acidic/alkaline contaminants on the rupturedisk may lead to undesired corrosion, thereby causing the disk to ventat below-design pressure conditions.

In addition, the rinse line provides a means to halt sample cookingwhile the digestion apparatus is cooled. In previously known digestionapparatuses, as discussed above, an operator must allow the digestionapparatus to cool to a manageable temperature before removing the samplecontainer from the digestion chamber for rinsing. As the apparatuscools, the sample may continue to cook. In contrast, the rinse line maybe used effectively to quench the sample and optionally remove digestionfluid therefrom. Rapid quench-cooling the sample enhances cookingprecision.

Pressure Relieving Means and Condenser

As alluded to above, a condenser may be used with digestion apparatuses.A condenser is a device or unit used to condense a substance from itsgaseous to liquid state, typically by cooling the substance. In sodoing, the substance releases its latent heat which is typicallytransferred to the condenser coolant. Exemplary coolants include waterand air.

In the context of the present invention, condensers are typically usedto facilitate functions such as digestion fluid extraction and/or vaporsampling temperature liquor during the cooking cycle. As shown in FIG.1, when valve 404 is opened, an external condenser 400 may fluidlycommunicate via conduit 402 and 406. As a result, fluid from chamber 30may be cooled by condenser 400 before being extracted therefrom viaconduit 408 by opening valve 410.

Also as alluded to above, digestion apparatuses are often constructedwith components that serve as pressure relieving means. For example,pressure release valves may allow for controlled venting of thedigestion chambers to ensure control over pressure therein. Similarly,rupture disks may serves as a safety mechanism to ensure that anyexcessive pressure buildup in the chamber does not lead to explosive orcatastrophic failure. In any case, the operation of pressure relievingmeans is typically accompanied by the release or discharge of hotpressurized digestion fluid. Such fluid may represent an operationalhazard.

To reduce the dangers associated with pressure relieving means, theinvention provides a digestion apparatus as generally described hereinin combination with a condenser interfaced with the fluid transportingsystem and/or chamber. The condenser may be placed downstream from thepressure-relieving means to allow for fluid released therefrom to draininto the condenser. For example, as shown in FIG. 1, the condenser isinterfaced with the rupture disk 114 via conduit 202. As discussed below(not shown), vent valve 116 may also be interfaced via a detachableflexible hose upstream from condenser 400 as well. As a result, thecondenser may cool the released fluid for ease of handling.

Pressure relieving means in combination with condenser may sometimes beused improve certain digestion processes. For example, cellulosic andother samples often outgas as they are brought to a cooking temperaturein a digester. Such outgassing may compromise the performance of thedigester. In some instances, outgassing may contribute to theirregularity of digestion fluid flow. In addition or in the alternative,outgassing may contribute to undesirable overpressurization within thevessel chamber. In turn, desired digestion reactions may be hindered ortheir rates compromised.

To avoid such outgassing problems, some operators have resorted to aproblematic technique that involves preheating a sample and digestionfluid within an open digester. Instead sealing the vessel beforeapplying heat, the lid is left off the digestion vessel until the afterthe sample has had some time to outgas as the temperature is ramped up.This is problematic for a number of reasons. First, as heat is appliedto the sample and digestion fluid, the sample is not the only source ofvapor generation. Vapors of the digestion fluid may be produced, e.g.,via evaporative processes, as well. Because such vapors may be caustic,acrid and/or noxious in nature, the practice of such a techniquerequires, at a minimum, a ventilation hood or some other means to drawsuch vapors away from the operator. Splatter and other heat relateddangers associated with an open-digester precook also make thistechnique undesirable.

In some embodiments, a pressure relieving means may be provided toaddress outgassing problems without resorting to preheating a sample inan open vessel. For example, a vent valve may be used to allow outgassedvapor to be released from a sealed vessel. Typically, such a vent valveis interfaced with the chamber at a location not susceptible tosubmersion by sustained contact with, or pooling by digestion fluid.Thus, such a vent valve may be interfaced with a port located above theinlet port and/or fluid distribution means. Optionally, the vent valvemay be interfaced with a port extending through the vessel closure.

In operation, a sample is placed within the vessel, and the digestionchamber is sealed. As heat and digestion fluid is directed toward thesample, sample outgassing may increase the chamber pressure. Thus, thevent valve may be opened to relieve such pressure buildup. In someinstances, the valve may be opened manually. Alternatively, the valvemay be opened automatically in a periodic, as-needed, and/orpredetermined manner according to the temperature and/or pressure of thechamber. In any case, a flow path, e.g., in the form of flexible tubing,may be provided between the vent valve and the condenser to avoid adangerous and uncontrolled spray of hot digestion fluid as the ventvalve is opened. Optionally, quick disconnect fitting technology, i.e.,technology designed for use with components that are moved often andwithout disrupting system fluid pressure or compromising safety, may beused so as to avoid uncontrolled flow of digestion fluid as the whentubing is being connected or disconnected from digestion chamber, e.g.,at the vent valve, and/or from the condenser.

The invention may include one or more condensers. When a plurality ofcondenser is employed, each condenser may serve a different purpose. Forexample, distinct condensers may be used for sampling and safetypurposes. Each of a plurality of pressure relieving means may be made tocommunicate with different condensers.

Digestion Fluid Transportation

Among other inventive facets described herein, the manner in whichdigestion fluid is transported represents another novel and nonobviousaspects of the invention for a number of reasons. As alluded to above,irregular digestion fluid flow is generally an undesirable event thatmay be mitigated via pump priming. In addition, as discussed in U.S.Pat. No. 7,811,416 and U.S. Patent Application Publication No.20100329943, digestion fluid distribution means such as nozzles havebeen observed to increase the velocity and dispersion of white liquorand/and other fluids in digestion apparatuses to increase penetration ofsuch fluids into sample fibers. It has now been discovered thatirregular fluid flow may be particularly detrimental to the performanceof vertically circulating digestion apparatuses in general as well assuch digestion distribution means in particular.

The fluid-transporting system may be constructed to reduce irregularfluid flow. As shown to FIG. 1, vertically circulating digestionapparatuses 10 are constructed with a fluid-transporting system thatuses a pump 110 to direct fluid from a drain 109 at a lower elevationthrough a flow path that travels upward to an inlet port 102 at a higherelevation. As such, the flow path must typically exhibit at least onebend.

It has been discovered that the bend 329 in the flow path immediatelypreceding the inlet port 102 can be a source of irregular flow. Sharpbends tend to contribute to irregular fluid flow to a greater degreethan more gradual bends. While not wishing to be bound by theory, itappears that gas bubbles tend to accumulate at such an elevated bend.Bubbles have been observed to disrupt laminar fluid flow.

FIG. 7 provides photographs of an upper portion of an exemplarydigestion apparatus of the invention fluid-transporting system having anexperimental verified improved fluid flow. As shown in FIG. 7A, fluid700 emerging from the inlet 102 may be maintained in laminar flow. FIG.7B highlights the plumbing associated with the flow path upstream fromthe inlet port. Notably bend 329 in the flow path immediately precedingthe inlet 102 is gradual rather than sharp in nature.

Thus, in another embodiment, the invention provides a digestionapparatus as generally described herein with an improvedfluid-transporting system adapted to direct fluid out of the digestionchamber back into the digestion chamber. The fluid-transporting systemdefines a flow path that ensures substantial laminar digestion fluidflow through the inlet port. For example, the flow path may extendthrough, in order, a submerged outlet port, a pump, a heat exchanger,and a conduit that immediately precedes an inlet port. When the conduithas a diameter about 1 centimeter, the conduit may define a flow paththat exhibits no bend having a radius of curvature less than about 1centimeter. Preferably, the flow path may exhibit no bend having aradius of curvature less than about 2 centimeters. Persons of ordinaryskill in the art should be able to scale flow path diameters and radiiof curvature accordingly upon routine experimentation in view of thedisclosure contained herein.

Another contributory source of irregular fluid flow can be found in howfluid is fed from the vessel to the pump. As discussed above, it istypically desirable to provide the pump with a well-developed inlet flowso that the pump meets its potential. One way this may be done, as shownin FIG. 1, by placing the pump such that its inlet is located directlybelow the outlet port 108 of the vessel 20 and a substantially lineardownward flow path is formed from the outlet port 108 to the pump 110.

However, as discussed above, an offset pump placement may be used. Forexample, the flow path between the outlet port 108 and the pump 110should avoid sharp turns, e.g., those associated with 90° fittings.Instead, as shown in FIG. 10, a conduit 320 forming gently curving flowpath of appropriate cross-sectional area may be employed to provide awell-developed and substantially bubble free flow to the impeller ofpump 110 located with an offset placement relative to the outlet port ofthe digestion vessel. For example, the flow path exiting from thechamber 30 from the vessel outlet port 108 may begin in a substantiallyvertically downward direction but enter the pump 110 in a substantiallyhorizontal direction.

As discussed above, a pump may not perform or be as reliable as expecteddue to a faulty intake plumbing layout. When poorly developed flowenters the pump, mechanical problems arising from cavitation andvibration may occur. Similarly, premature seal, bearing and impellerfailure may also occur. As a result, the operation of digester may beaccompanied with high maintenance costs, high power consumption, andless-than-specified head and/or flow, as well as imprecise cooks due tolack of liquor flow.

Thus, in yet another embodiment, digestion apparatus as generallydescribed above is provided. The fluid-transporting system is adapted todirect fluid out of the digestion chamber back into the digestionchamber through a flow path that extends, in order, through a submergedoutlet port, a pump, and an inlet port. The flow path between outletport and the pump may have a diameter of about 1 centimeter and exhibitno bend having a radius of curvature less than about 2 centimeters.Optimally, any bend present in the flow path may exhibit a radius ofcurvature of at least about 4 centimeters. Persons of ordinary skill inthe art should be able to scale flow path diameters and radii ofcurvature accordingly upon routine experimentation in view of thedisclosure contained herein.

When the pump is constructed to receive fluid from a horizontal flowpath segment, the pump may be located below the submerged outlet port inan offset manner. The pump should be offset from the outlet port at asufficient distance to avoid pump cavitation problems. For example, ithas been experimentally demonstrated that for a particular digestionapparatus that employs a flow path having a horizontal segment of about8 centimeters in length immediately preceding the pump, the apparatus'spump tends to exhibit cavitation problems at about 185° C. whendigestion fluid of a particular viscosity is circulated. In contrast,the same digestion apparatus filled with the same digestion fluid may beoperated at a substantially higher temperature, e.g., above about 210°C., when the horizontal segment is increased in length to about 50centimeters.

To have a well-developed flow pattern, then, it may be preferable tohave a substantially straight and horizontally oriented flow pathsegment of a length of at least about 15 to 20 times the diameter of thepump's intake port. Preferably, the straight horizontal segment of theflow path immediately preceding the pump is of a length of at leastabout 50 to about 65 times the diameter of the pump's intake port.

Multicompartment Container

In another embodiment, the invention provide an apparatus generallydescribed herein except that it includes a container within thedigestion chamber, the container comprising a plurality of compartmentsfor holding a plurality of samples. Such a container may be used toensure that a plurality of different samples can be processed undersimilar or identical conditions during the same experimental run. As aresult, some of the samples may serve as an “experimental control” whilethe other(s) may serve as an “experimental variable.”

FIG. 8 schematically depicts different containers having a plurality ofcompartments of substantially identical shape and size. FIG. 8A depictsa container 60 in the form of a basket having a cross-shaped divider 61therein resting on the basket's bottom 66. The divider 61 thatvertically separates the basket into four compartments, 63A, 63B, 63C,and 63D. Optionally, the divider may be removable from the basket.

FIG. 8B depicts a container 60 having three horizontally separatedcompartments 63A, 63B, and 63C. Each compartment 63A, 63B, and 63C has acorresponding bottom 66A, 636, and 66C made from a mesh or other porousmaterial. The mesh material is typically selected to ensure that samplescontained in the compartments do not fall through the mesh, and mayvary, e.g., in wire and hole size.

Thus, additional container constructions are possible. For example, thenumber of compartments may be increased or decreased as needed. Inaddition, the dividers may be rigid or flexible. In some instances,porous sacks, pouches, and the like may be used to compartmentalizedifferent samples within the container.

Tapered Vessel Chamber

As discussed above, the fluid-transporting system may be constructed toreduce irregular fluid flow associated with the digestion apparatus ofthe invention. It has now been discovered that the construction ofdigestion vessel and chamber may also affect fluid flow. In particular,it has been discovered that vessels forming a digestion chamber thatexhibits a tapered lower portion may be advantageously used to effectfluid transfer.

FIG. 12 depicts various vessel designs for the inventive digestionapparatus. Each vessel 20 of FIG. 12 has an upper sidewall 21 thatdefines a substantially cylindrical portion of a chamber 30. However,the vessels exhibit different base constructions. FIG. 12A depicts avessel design with a flat base 24. FIGS. 12B and 12C depict a vesseldesigns with tapered bases 24. In particular, FIG. 12B depicts a vesseldesign associated with a chamber having a lower portion that exhibits asubstantially conical geometry, and FIG. 12C depicts a vessel designassociated with a chamber having a lower portion that exhibits asubstantially hemispherical geometry.

As shown, container 60 is located within chamber 30. Optional feet 65 isprovided to raise the bottom of container 60 from the base 24 of thevessel of FIG, 12A. Alternatively, as shown in FIGS. 12B and 12C, thecontainer may rest on the taper base 24 of vessel 20.

In operation, as fluid is introduced into the chamber 30, the fluidflows downward, pooling at a lower portion 31 of the chamber 30. Inturn, the pooled fluid may flow out of the chamber 30 via outlet port108 and drawn through conduit 320 toward pump 110. Depending on howfluid is introduced into the chamber 30 and how fluid flows throughsample material in the container 60, fluid pooled at the lower portion31 of the chamber may exhibit turbulence, and/or other phase and/orcompositional variations such as bubbles and particular matter inliquor.

It has been experimentally verified that the vessel design shown in FIG.12C provides improved fluid flow to the pump relative to the vesseldesign 12A. For example, digestion apparatuses with the improved designmay be run at higher temperatures, pressures, and/or flow rates. Whilenot wishing to be bound by theory, the improved design may provide welldeveloped flow to the pump in different ways. For example, it ispossible that the taper design provides funnel-type functionality toprovide improved liquid channeling performance. In addition, it ispossible the tapered geometry tends to increase the depth of pool fluid,thereby reducing the effect of surface turbulence and associated bubblegeneration (particularly when liquors containing surfactants are used)on fluid flow to the pump.

Thus, in a further embodiment, a digestion apparatus is provided asgenerally described above. However, the digestion chamber exhibits atapered lower portion. For example, the tapered lower section may have asubstantially conical or hemispherical geometry. The fluid-transportingsystem may be adapted to direct fluid out of the digestion chamber backinto the digestion chamber through a flow path that extends, in order,through a submerged outlet port at the tapered base, a pump, a conduitand an inlet port. In such a case, the fluid-transporting system definesa flow path from the outlet port to the pump in a manner that ensuressubstantially steady pressure for fluid emerging from the pump.

Variations on the Invention

Variations of the present invention will be apparent to those ofordinary skill in the art in view of the disclosure contained herein.For example, the inventive apparatus may be designed to run on a numberof different power sources. Direct current power sources, e.g., batterypowered and/or alternating current power sources, e.g., 110V, 230V,380V, single phase, may be used to power various components of theinventive digester. Additionally, the fittings described above may useall male, all female, or a combination of male and female connections.

In addition, the invention may be used to carry out chemical reactionsother than digestion and/or may serve as a part of a process that usesthe sample digested. For example, the invention may be used to carry outchemistries associated with the conversion of sample materials such ascarbohydrates, polysaccharides, and cellulosic materials into productssuch as alcohols, acrylates, ketones, etc. As another example, thefluid-transporting system of the invention may be adapted to circulateyeast or other solutions that may be required to produce alcohol,optionally through fermentation. Similarly, when it is desirable toprevent oxidation of alcohols in the inventive apparatus, inert gasand/or vacuum technologies may be used to ensure that any chamberscontaining alcohol are free from the presence of oxygen or otheroxidizing agents.

Accordingly, plumbing components may vary as well. In general, plumbingcomponents must be selected to withstand chemistries associated with thedigestion process. Thus, for example, digesters designed for digestionprocesses employing highly corrosive digestions fluids at elevatedtemperatures may require the use of stainless steel tubing and valves.However, the invention does not necessarily require rigid plumbingcomponents. Flexible tubing may be used in a number of situations. Forexample, flexible tubing may be used to connect the digesters of theinvention to water and digestion fluid supplies or to effect controlleddrainage of fluid from the digester. An optional flow meter also canhelp control the flow rate in the bypass line or main circulation line.

It is to be understood that, while the invention has been described inconjunction with the preferred specific embodiments thereof, theforegoing description merely illustrates and does not limit the scope ofthe invention. For example, while the foregoing description focuses onthe invention in a batch-processing context, the invention may also beof use in a continuous processing context. By incorporation fluidextraction and/or injection technologies, the inventive apparatus may beadapted to simulate continuous processes as well.

In any case, additional variations of the invention may be discovered,e.g., upon routine experimentation, without departing from the spirit ofthe present invention. For example, the inventive apparatus may beconstructed to contain or exclude specific features and componentsaccording to the intended use of the apparatus, and any particularembodiment of the invention, e.g., those depicted in any drawing herein,may be modified to include or exclude element of other embodiments.Alternatively stated, different features of the invention describedabove may be combined in different ways. Other aspects, advantages, andmodifications within the scope of the invention will be apparent tothose skilled in the art to which the invention pertains.

All patents and patent applications disclosed herein are incorporated byreference in their entirety to an extent not inconsistent with the abovedisclosure.

1. A digestion apparatus, comprising: good a vessel having a digestionchamber therein and an opening that provides access to the digestionchamber; a closure adapted to interface with the vessel opening to forma fluid-tight seal against a digestion pressure and temperature withinthe chamber; a fluid-transporting system adapted to direct fluid out ofthe digestion chamber back into the digestion chamber through an inletport; and a fitting having at least five fitting ports in fluidcommunication with each other, at least one fitting port interfaced withthe vessel, closure, and/or fluid-transporting system.
 2. The apparatusof claim 1, wherein at least three fitting ports define substantiallycoplanar fitting passageways.
 3. The apparatus of claim 2, wherein atleast two of the substantially coplanar fitting passageways are notparallel to each other.
 4. The apparatus of claim 2, wherein nosubstantially coplanar fitting passageways is a parallel to another. 5.The apparatus of claim 1, wherein the fitting has exterior surfaces thatdefine a prism.
 6. The apparatus of claim 5, wherein the prism has asquare or rectangular base.
 7. The apparatus of claim 1, furthercomprising a one-way valve interfaced with a fitting port.
 8. Theapparatus of claim 7, further comprising an additional vessel interfacedwith the one-way valve.
 9. A digestion apparatus comprising: a vesselhaving a digestion chamber therein and an opening that provides accessto the digestion chamber; a closure adapted to interface with the vesselopening to form a fluid-tight seal against a digestion pressure andtemperature within the chamber; a fluid-transporting system adapted todirect fluid out of an outlet port of the digestion chamber, past aheater, through an inlet port, and into the chamber; a condenserinterfaced with the fluid transporting system and/or chamber; and apressure-relieving means for relieving any excessive pressure buildup inthe digestion chamber, the pressure-relieving means allows for fluidreleased therefrom to flow to the condenser.
 10. The apparatus of claim9, wherein the pressure-relieving means includes a rupture disk and/or apressure relief valve.
 11. The apparatus of claim 9, wherein thepressure-relieving means extends through the closure.
 12. The apparatusof claim 11, wherein the pressure-relieving means includes a valve. 13.The apparatus of claim 9, wherein the pressure-relieving means fluidlycommunicates with the condenser via flexible tubing.
 14. The apparatusof claim 13, wherein the flexible tubing is connected to thepressure-relieving means and/or the condenser via quick disconnectfitting.
 15. A digestion apparatus, comprising: a vessel having adigestion chamber therein and an opening that provides access to thedigestion chamber; a closure adapted to interface with the vesselopening to form a fluid-tight seal against a digestion pressure andtemperature within the chamber; and a fluid-transporting system adaptedto direct fluid out of the digestion chamber back into the digestionchamber through a flow path that extends, in order, through a submergedoutlet port, a pump having an intake port of an intake port diameter,and an inlet port, wherein and the pump is located below the submergedoutlet port in an offset manner and the flow path between outlet portand the pump exhibits a substantially horizontal segment of a lengththat is at least about 20 times the intake port diameter.
 16. Theapparatus of claim 15, wherein the length of the substantiallyhorizontal segment is at least about 50 times the intake port diameter.17. A digestion apparatus, comprising: a vessel having a digestionchamber that exhibits a tapered lower portion and having an upperopening that provides access to the digestion chamber; a closure adaptedto interface with the vessel opening to form a fluid-tight seal againsta digestion pressure and temperature within the chamber; and afluid-transporting system adapted to direct fluid out of the digestionchamber back into the digestion chamber through a flow path thatextends, in order, through a submerged outlet port at the tapered base,a pump, a conduit and an inlet port, wherein the fluid-transportingsystem defines a flow path from the outlet port to the pump in a mannerthat ensures substantially steady pressure for fluid emerging from thepump.
 18. The digestion apparatus of claim 17, wherein the tapered lowersection has a substantially conical geometry.
 19. The digestionapparatus of claim 17, wherein the tapered lower section has asubstantially hemispherical geometry.
 20. A digestion apparatus,comprising: a vessel having a digestion chamber therein and an openingthat provides access to the digestion chamber; a closure adapted tointerface with the vessel opening to form a fluid-tight seal against adigestion pressure and temperature within the chamber; afluid-transporting system adapted to direct fluid out of the digestionchamber past a heater through an inlet port into the chamber; and arinse line in fluid communication with the inlet port via a check valve.21. The apparatus of claim 20, further comprising a means fordistributing fluid located downstream from the inlet port.
 22. Theapparatus of claim 21, wherein the means for distributing fluidcomprises a fluid-conveying member having a plurality of perforationthrough which fluid may flow.
 23. The apparatus of claim 22, wherein thefluid-conveying member comprises a tube having a lumen extending from anopen proximal terminus attached to the port to a closed distal terminusand the perforations fluidly communicates with the lumen.
 24. Adigestion apparatus, comprising: a vessel having a digestion chambertherein and an opening that provides access to the digestion chamber; aclosure adapted to interface with the vessel opening to form afluid-tight seal against a digestion pressure and temperature within thechamber; a fluid-transporting system adapted to direct fluid out of thedigestion chamber past a heater through an inlet port into the chamber;a first temperature sensor that monitors vapor temperature in thechamber at or near the closure; and a second temperature sensor thatmonitors fluid temperature within the fluid-transportation system and/orin a submerged portion of the chamber.
 25. The apparatus of claim 24,further comprising a signal generator that generates a detectable signalwhen the first temperature sensor detects a vapor temperature thatexceeds a fluid temperature detected by the second temperature.